1. Field of the Invention
The present invention relates to a method and an apparatus for detecting an optimal writing power for recording user data on a writable optical recording medium.
2. Description of the Related Art
FIG. 1 is a simplified block diagram of a conventional apparatus for recording data on a writable optical disk. The apparatus comprises an A/D converter 20 for digitizing an analog signal, an MPEG encoder 30 for encoding the digitized data into the MPEG format, a digital recording signal processing unit 70a for converting the MPEG-formatted data into recording-formatted EFM (Eight to Fifteen Modulation) data while adding additional data such as error correction codes, a channel bit encoder 80 for converting the recording-formatted data into writing signals, an optical driver 81 for yielding signals to drive a LD (laser diode), an optical pickup 11 for recording signals onto surface of a writable optical disk 10 and reproducing recorded signals from the optical disk 10, a driving unit 90 for driving the optical pickup 11 and a motor M to move and rotate respectively, an R/F unit 100 for equalizing and shaping the signals reproduced by the pickup 11 to produce binary signals, a servo unit 110 for controlling the driving unit 90 based upon a tracking and a focusing error signal provided by the pickup 11 and the rotation speed of the optical disk 10, a digital reproduced signal processing unit 70b for restoring compressed data from the binary signals using a self clock synchronized with the binary signals in phase, an MPEG decoder 120 for restoring original video and/or audio data by decoding the compressed data, and a microcomputer 60 for controlling overall operation of recording and reproduction.
Upon receiving a request for recording user data, the microcomputer 60 controls the pickup 11 through the servo unit 110 and the driving unit 90 to read the indicative target writing power recorded on the writable disk medium 10. In case where the disk 10 is a rewritable recording medium such as a CD-RW, the target writing power is recorded as 3-bit data W1,W2, and W3 in the M1 information byte in the field of ATIP (Absolute Time In Pre-Groove) located in the lead-in area of the optical disk 10. FIG. 2 shows the recording format of the bits ‘W1W2W3’ and the meaning of each value.
After reading the target writing power data W1,W2, and W3, that is, the indicative target writing power Pind, recorded as above, the microcomputer 60 transfers predetermined test data, for example, a byte of 10101010, to the channel bit encoder 80 through the digital recording signal processing unit 70a. For recording digital bit streams outputted from the digital recording signal processing unit 70a, the channel bit encoder 80 converts the bit streams into PWM (pulse-width-modulated) signals and applies the modulated signals to the optical driver 81.
The microcomputer 60 applies power adjusting data to the optical driver 81 and changes its value in sequence as shown in FIG. 3 for changing the writing power within a given range with respect to the read target writing power whose intensity is assumed to 8 mW in FIG. 3. In response to the power adjusting data, the optical driver 81 outputs writing signals whose power corresponds to the applied power adjusting data so that the pickup 11 records the digital bit streams for testing in the test area of the optical recording medium 10. In the case where the optical recording medium 10 is a rewritable CD such as a CD-RW, the test data are recorded in test area A of the PCA (Power Calibration Area) as shown in FIG. 4.
Along with recording the digital bit streams for power testing, the microcomputer 60 controls the optical pickup 11 to write null data of one ATIP in the count area B located in the PCA to indicate how many times test writing is accomplished. For example, if this recording of the digital bit stream for power testing is executed thirdly for the disk 10, the null data are written to the third ATIP of the count area B located in the PCA as shown in FIG. 4 to indicate that test operations were executed three times.
On the condition that the test data have been recorded in the test area A of the PCA with the varying writing power, the microcomputer 60 controls the pickup 11 to reproduce the most recently recorded digital bit streams for power testing. While reproducing the test data, the microcomputer 60 keeps detecting the jitter magnitude of the binary signals converted from the reproduced RF (Radio Frequency) signals by the R/F unit 100. Then, if the detected jitter magnitude is lowest, the microcomputer 60 determines the writing power used to record the test data whose jitter magnitude is lowest as an optimal writing power for the disk 10. That is, the power Pop is chosen to optimal in FIG. 3.
If external video and/or audio signals are received for recording after the optimal writing power Pop is determined, the received video and/or audio signals are digitized by the A/D converter 20 and encoded into the MPEG formatted data by the MPEG encoder 30. The digital recording signal processing unit 70a generates digital bit streams modulated from the encoded data and error correction codes added to the encoded data by itself. The channel bit encoder 80 converts the digital bit streams into PWM signals and applies the modulated signals to the optical driver 81 to record the modulated bit streams to the disk 10.
Meanwhile, the microcomputer 60 sets the optical driver 81 to generate a driving current corresponding to the optimal writing power Pop obtained through the previous procedure. Therefore, the PWM signals whose power is optimal for the disk 10 causes the received data to be recorded in the program area of the optical disk 10.
In the above-explained conventional method for recording data on an optical disk, when a request is received for recording new data successively from the record-ending point of the program area after a previous data recording operation is done, the microcomputer 60 performs the afore-mentioned OPC (Optimal Power Calibration) again. In other words, the microcomputer 60 repeats the OPC whenever a request for recording additional data is received.
However, the OPC needs to move a pickup inwardly and outwardly, that is, between PCA and program area. This takes a relatively long time to start data recording, and delays the data recording operation.
Moreover, since the test area A of PCA for an optimal writing power calibration is located inwardly from a lead-in area of the program area of an optical disk where user data are to be recorded, the characteristics of recording environment of the program area may be different from that of the test area. Accordingly, sometimes an optimal writing power detected from the test area is not optimal for the recording area where user data are to be written.